In Vitro Neurotoxicity Comparison: Colistimethate Induces Higher Toxicity Than Colistin via Formaldehyde Accumulation.

Abstract

Colistin as a last-line of defence for treating multidrug-resistant Gram-negative bacterial pathogens, is most commonly administered as its inactive prodrug, colistimethate (CMS), for its reduced nephorotoxity. However, the neurotoxicity of CMS compared to colistin has not been studied. In this study, we conducted cell viability assay and discovered that 0.3 mM CMS demonstrated higher toxicity to human neural SH-SY5Y cells compared to 0.3 mM colistin. The concentration of CMS used in this study was six times the average in vivo concentration. Next, we identified formaldehyde as a significant contributor to the observed toxicity, independent of colistin. We employed LC-MS/MS to measure colistin levels resulting from CMS hydrolysis over time, alongside a kit to quantify formaldehyde production from CMS. RNA-seq analysis of SH-SY5Y cells treated with CMS and colistin revealed that DNA damage and cell cycle pathways were notably affected by CMS-induced neurotoxicity, aligning with previous findings related to formaldehyde treatment. Our results indicate that CMS is more cytotoxic to neural cells than colistin, raising concerns about its potential to impair brain function. Given these findings, careful consideration is warranted before administering high doses of CMS directly to the CNS via intrathecal or intraventricular routes.